Conventionally, when an electronic circuit board or the like is produced, it has been common to form a metal film on the surface of a substrate to form a metallic circuit pattern thereon. For example, as a film formation technology for forming such a metal film, there has been proposed a film formation technology that includes forming a metal film on the surface of a Si semiconductor substrate or the like through a plating process such as an electroless plating process (for example, see Patent Literature 1), or forming a metal film using PVD such as sputtering.
However, when a plating process such as an electroless plating process is performed, it has been necessary to perform washing after the plating process, as well as a process of processing a waste liquid that has been produced during washing. Meanwhile, when a film is formed on the surface of a substrate using PVD such as sputtering, internal stress is generated in the metal film formed. Thus, there is a limitation in increasing the thickness of the film. In particular, when sputtering is performed, it has been possible to form a film only in a high vacuum in some cases.
In view of the foregoing, there has been proposed a film formation method for forming a metal film that uses a positive electrode, a negative electrode, a solid electrolyte membrane disposed between the positive electrode and the negative electrode, and a power supply unit that applies a voltage across the positive electrode and the negative electrode (for example, see Non Patent Literature 1).
The solid electrolyte membrane herein is formed by spin-coating the surface of a substrate with a solution containing a precursor of the solid electrolyte membrane in advance and curing the solution and then impregnating the resulting membrane with metal ions to cover the surface of the substrate. Then, the substrate is disposed such that it is opposite the positive electrode and is electrically connected to the negative electrode, and a voltage is applied across the positive electrode and the negative electrode, so that the metal ions that have impregnated the solid electrolyte membrane are deposited on the negative electrode side. Accordingly, a metal film made of metal of the metal ions can be formed.